Determining movement and position of moving objects



March 18, 1930. E. 1. GREEN 1,750,653

DETERMINING MOVEMENT AND POSITION OF MOVING OBJECTS Filed Dec. 1927 jlfam'ig Studio/r0 C Fixed Staa' w J INVENTOR. Z. I GKEB/fl/ A TTORNEY Patented Mar. 18, 1930 UNITED STATES PATENT OFFICE ESTILL I. GREEN, OF EAST ORANGE, NEW JERSEY, ASSIGNOB TO AMERICAN A TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK DETERMINING MOVEMENT AND POSITION OF MOVING OBJECTS Application filed December 8, 1927. Serial No. 238,546.

This invention relates to methods and systems for determining, with precision, the location of a moving object and the speed and direction of its travel. The invention has particular application to such moving objects as aeroplanes and ships, where it is difficult to determine the location and speed of travel due to the lack of nearby fixed objects, but it will be readily understood that the invention is applicable to other cases than those mentioned.

In general, the invention involves the transmission in both directions between fixed and moving stations of frequencies whose phase is definitely related to a frequency generated at the observing station. At the ob serving station a comparison is made between the phase of the frequency generated at that station andthe phase of a frequency which has been shifted in phase by transmission. In

general, this phase shift is produced by tandem transmission from the observing station to a distant station and then back again. The transmission in the two directions preferably '25 takes place at different frequencies.

The position of the moving object within one wave length may be determined by noting the phase adjustment necessary to bring the compared frequency components lnto phase with each other. The exact distance between the two stations may be determined by varying a frequency at the observing station over such a range as will produce one cycle of phase change at the observing polnt.

The distance may then be determined by a simple formula from the observed frequency range.

Having determined the distance between the moving object and one fixed station, by a similar process the distance between the moving object and another fixed station may be observed. Knowing the distance between the two fixed stations, the position of the moving station is thus determined absolutely.

As the moving station passes along its course, cyclic phase changes between the compared frequency components occur at the observing station. As one of these cyclic changes of phase occurs each time the obyect moves with respect to the fixed station a distance equivalent to a wave length derived from the frequencies transmitted, the speed with reference to the fixed station may readily be determined. Knowing the location of the moving object with respect to two fixed stations and the speed with respect to each station, the absolute speed and direction of travel may be determined by simple trigonometric relations.

The invention will now be more fully understood from the following detailed description when read in connectionwith the accompanying drawing, in which Fig. 1 is a diagram illustrating how the location of a moving object and its direction of travel may be determined; Fig. 2 illustrates a circuit arrangementwhich may be used in connection with the invention, and Fig. 3 illustrates another form of the invention.

Fig. 2 illustrates one arrangement by which a precise location may be determined. Here, a frequency f is generated from the moving station by means of an oscillator 0 and, by means of a modulator M modulates a fre quency f generated by an oscillator 0 The frequency 2, and its side frequencies f f and f f are transmitted through a selective device TF and impressed upon a transmitter CT, by means of which the frequencies are radiated to the fixed station A. At this point, they are picked up by the radio receiving apparatus AR, and, by means of a demodulator D2, the frequency f, is again derived therefrom, this frequency being selected from the other frequencies resulting from the demodulating operationby means of a selectl"6 device RF' Through the agency of the modulator M the frequency f thus obtained modulates a frequency f generated at the station A by means of an oscillator 0 The resultant frequencies f f f and fg 'f1 are then passed through a selective device TF and, by means of transmitting apparatus AT at the station A, are radiated to the moving station. At the moving station, these frequencies are demodulated by the demodulator D and the resultant frequency f, is selected by the selective device RF The phase of the resultant frequency f is then compared with that of the original frequency f gen- 190 L a-i erated by the oscillator 0 by means of a balanced rectifier combination comprising vacuum tubes 20 and 21, connected in such a man ner that an indication of their relative phase relations is obtained for certain particular phase difit'erences regardless of their comparative amplitudes. It will be seen that the arrangement of the balanced rectifier is such that when the two inputs differ in phase by 90, the indication on the output meter 22 will be zero. When the inputs differ in phase by 180, the current registered by the galvanometer 22 will be a maximum in one direction. For a 270 phase difference, the indication will again be zero, while for a 360 phase difference it will be a maximum in the opposite direction.

If, now, the frequency f at the moving station remains fixed while the object is in motion, it is clear that the speed of travel with reference to the fixed station may be determined as follows:

The phase shift produced in the frequency f due to transmission over the distance a between stations C and A is Q o X 360 where A. is the wave length corresponding to f Similarly the phase shifts corresponding to the frequencies f f and f i are X 360 M X 360 and I l O l O X 360 M X 360 1 f Hence the phase shift produced in the frequency f is xsem- M Similarly the phase shift resulting from transmissionfrom A to G will likewise be so the total phase shift for the complete'transmission path will be 2a 0 I X 360 From the foregoing, it follows that when the moving object increases or decreasesuts distance from the fixed station by an amount equal to the wave length the galvanometer will record one cycle. Then if K be the number of recorded cycles, K5 is the speed of the moving object with reference to the fixed station A. And hence, if a is the angle between the line joining the moving object to the fixed station and the direction of travel of the moving object, the actual speed S will depend upon the relation 8 cos a=K (1) vthe fixed station is then determined as follows:

The phase shift at frequency f' in transmitting from the moving station to the fixed station, is

L 0 f l X 360 Similarly, the phase shift at f" is a O j l X 360 the preceding expression is equal to 360. Therefore, we may write from which we getv It is assumed in the previous discussion that the phase shift of the apparatus is independent of frequency in the range required for the variation of f If the apparatus does not normally have this characteristic, it may be given such characteristic by the use of known phase equalizing means. By means of the above equation, the absolute distance travel and the direction of the fixed station B) and in terms of a wave length corresponding to the frequency f transmitted between station C and station B. This equation is 8' cos B=K (2) We now have an absolute determination of the distances a and b, and, knowing the distance between the station A and station B, the absolute position of the moving station is given by means of a triangle similar to that of Fig. 1. Knowing the sides of this triangle, the angle 4 between the sides of the triangle is at once given, and from the relation fi together with equation (1) and the corresponding equation (2) in terms of B and a the values of S, u and B may be determined. We will then have an absolute determination of the speed, direction of motion, and location of the moving object. I

It will be noted that instead of shifting one of the frequencies to determine the distance a or b as the case may be, the phase ad- 'uster 23 may be adjusted instantaneously to ring the two components applied to the alanced detector in phase with each other. The extent of this adjustment gives the location of the moving object within some one wave length.

If the frequency f is made small so that the wave length is relatively large, it will, in general, be quite possible to determine the particular wave length in which the movin object is located, particularly if the observer has in advance a general 1dea of his position. For example, if the frequency i, were 1,000 cycles, one wave length would correspond to 180 miles, and the location of the object within-the proper 180 miles would not i be difiicult to determine with some previous knowledge of the general location. However, as will now be pointed out, other features may be utilized to assist in this determination.

As an aid in determining the articular wave length in which the movin o ject is located, loops or other direction ding apparatus. of known character may be employed to indicate the approximate direction of each of the fixed statlons. Thus 0:, the angle between the direction of travel and the direction of the fixed station A, as well as B, the angle between the direction of travel and the drawn from the station C. If the deter mined angle is correct, these lines should pass through the fixed stations A and B.

Having determined the location of the moving station within some wave length corresponding to the frequency f as measured from station A', this fraction of a wave length will be laid out upon the line CA, as indicated at C-4n. Likewise, the location of the moving object in a wave length correspond-. ing to frequency f,, as measured from station B, is determined in the manner already stated, and this fraction of a wave length is laid out along the line CB, as indicated at (3-1). Additional wave lengths are then laid 01f, as indicated at n, 0, etc., in the one case, and r, 8, etc., in the other case. Since the distance from A to B is known,'this distance may be set to proper scale upon a pair of dividers, and, by means of the points of the dividers, corresponding wave length points on the line C'A and CB, which are separated by this distance, are then found. These points will then represent the location of the stations A and B with reference to the station C. I If, by the above method, no pair of points is found on the two lines which corres ond to the distance from A to B, the line B should ;be drawn through the two points which most nearly correspond to the distance A-B, and one of the lines AC or B-G should be shifted so that the points coincide.

By means of the relation I -=4 together with equations (1), and (2) the values of a, B and S may be determined. If the determined values of a and B check closely with those observed by means of the direction g finders, it may be assumed that not only will a, B and S, as determined from the equations, be correct, but also the distances A-C and B-C, as determined by the diagram, (Fig. 1), are correct. Thus, we will then have determined the location of the object with respect to stations A and B, its absolute speed S, and its direction of travel.

In determining the location of the moving object, it may be desirable to have the frequency f small. For the indication of speed of travel, however, it may be desirable to have a fairly large frequency in order to secure a readily observable number of cycles in a short period of time. The choice of frequencies can be made to fit the requirements of the particular case, and, if necessary, separate apparatus might be employed for the indication of position and 'for the indication of speed.

The method just described in connection with Fig. 2 may be simplified by using apparatus of the type illustrated in Fig. 3. Here, an unmodulated frequency f is generated by an oscillator 0 and is transmitted by the radio transmitter CT at the moving station G to the fixed station A. At the latter point, it is received by the radio receiver AR and impressed upon a harmonic producer AH thereat, which produces a second harmonic 2f This second harmonic is then transmitted by the radio transmitter AT at the fixed station A to the moving station, where it is picked up by the radio receiver CR. At the same time, the frequency f generated by the oscillator 0 at the moving station C is impressed upon a harmonic producer CH to produce a second harmonic 2; the phase of which is compared with the received second harmonic by means of a balanced detector arrangement similar to that of Fig. 2.

By analogy to equation (1), the speed of the moving object with reference to the fixed station will be The distance a to the fixed station A may be determined either b varying the phase shifter 23, as describe in connection with Fig. 2, or by varying the frequency f at the which may be expressed Likewise, the phase shift of frequency f" is The phase difference observedby means of the galvanometer at moving station 0 will be the difference between the phase shifts at the tlajwo frequencies f' and 7 and hence will X r h from which we get A AL . a 3 fg"'f2 3 (f j By usin similar apparatus to obtain similar data wit respect to another fixed station B,

cies in opposite directions, so that observa- I tions might be made both at the moving station and at the fixed station. It will also be evident that in case a very accurate indication can be obtained, by means of suitable direction finding apparatus, of the direction of a single fixed station, then the indications obtained by means of the waves transmitted between this fixed station and the moving station may sufl'ice to determine the location, speed and direction of travel of the moving object. It will also be understood that the apparatus, when not required for determinations of movement and position, may be used for communication purposes.

Obviously, the general principles herein disclosed may be embodied in many organizations widely different from those illustrated, without departing from the s irit of the invention as defined in the 0 lowing claims.

What is claimed is:

1. The method of ascertaining the movement and position of a moving object, which consists in transmitting electromagnetic waves between the moving object and a fixed station, comparing the phase of a wave as it arrives at the observing station with the phase of a wave as it appears at that point before transmission therefrom, thereby producing a resultant indication, changing the effective phase of one of the waves with respect to the other to produce a measurable instantaneous change of indication, thereby obtaining data from which the distance between the fixed station and moving object may be determined, observing the cyclic change in indication as relative phases of the two waves change with movement of the moving object through space, thereby obtaining data from which the speed of the moving object relative to the fixed station may be determined, and making similar observations with respect to waves transmitted between the moving object and a second fixed station, the complete data obtained enabling the computation of the absolute position of the moving object, its. direction of travel, and its absolute speed in such direction.

2. The method of ascertaining the position of a moving object, which consists in trans- .mitting electromagnetic waves between the moving object and a fixed station, comparing the phase of a wave as it arrives at the observing station with the phase of a wave as it appears at that point before transmission therefrom, thereby producing a resultant indication, changing the eifect-lve phase of one of the waves with respect to the other to prowaves transmitted between themoving object and a second fixed station, whereby the absolute position ofthe moving obj ect may be com uted. p

3 Tlie method of ascertaining the speed and direction of a moving object, which consists in transmitting electromagnetic waves between the moving object and a fixed station, comparing the phase of a wave as it arrives at the observing station, with the phase of a wave as it appears at that point efore transmission therefrom, thereby producing a resultant indication, observing the cyclic change in indication as the relative phases of the two waves change with movement of the moving object through space, thereby obtaining data from which the s eed of the moving object relative to the ed station may be determined, and making similar observations with respect to waves transmitted between the moving object and a second fixed station, the complete data obtained enablingthe computation of the direction of motion and absolute speed of the moving object in such direction when its position is known.

4. The method of ascertainin the movement and position of a moving ject, which consists in transmitting electromagnetic waves between a fixed station and the moving object, observing thetotal phase shift undergone by a wave in its travel, momentarily adjustmga circuit element acted upon one of the waves until a zero indication r sults, so that from the observed adjustment the position of the moving ob ect may be determined within a wave length corresponding to the frequency of the observed wave, observing the cyclic change in indication as the phase of the observed wave changes with movement of' the moving object through space, thereby obtaining data from wh1ch the speed of the moving ob ect relative to the fixed station may be determined, and makmg similar observations with respect to wayes transmitted between a second fixed statlon and the moving object, the complete data obtained enabling the computatlon of the absolute position of the moving object, its direction of travel, and its absolute speed in such direction.

5. The method of ascertaining the position f a mov g bj t, which consist 11. tra smitting electromagnetic waves between a fixed station and a moving object, observing the total phase shift undergone by a wave in 1ts travel, momentarily adjusting a circuit element acted upon'by one of the waves until a zero indication results, so that from the observed adjustment the position of the moving object may be determined within a wave length corresponding to the frequency of the observed wave, and making similar observa tlons with respect to waves transmitted between a second fixed station and the moving object, the complete data enabling the com putation of the absolute position of the moving obj ect when the distance between the fixed stationsand their direction from the moving station is known.

6. The method of ascertaining the speed and direction of a moving object, which consists in transmitting electromagnetic waves between a fixed station and a moving object,

observing the phase shift undergone by a wave in its travel, observing the cyclic change in indication as the phase of the observed wave changes with movememt of the moving object through space, thereby obtaining data from which the speed of the moving object relative to the fixed station may be determined, and making similar observations with respect to waves transmitted between a second fixed station and the moving object, the complete data obtained enabling the computation of the direction of motion and absolute speed of the moving object in such direction when its position is known.

7. ha system for ascertaining the movement and position of a moving object, means for transmitting electromagnetic waves between the moving object and talked station, means at one of said points to compare the phase of a wave as it arrives at said point with the phase of a wave as it appears thereat before transmission therefrom, means to change the efi'ective phase of one of the waves with respect to the other to produce an instantaneous change of the indicated con1parison, thereby obtaining data from which the distance between the fixed station and the moving object may be determined, means to indicate a cyclic change in the comparative phase of the two waves as the moving object moves throughspace, thereby obtaining data from which the speed of the moving object relative to the fixed station may be determined, means for transmitting similar electromagnetic waves between the moving object and a second fixed station, and means for making observations with respect to the waves so transmitted which are similar to those made with respect to the waves transmitted between the moving object and said first station, whereby data may be obtained enabling the computation of the absolute position of the moving object, its direction of travel, and its absolute speed in such direction.

8. In a system for ascertaining the position of a moving object, means for transmitting electromagnetic waves between the moving object and a fixed station, means at one of said points. for comparing the phase of a wave as it arrives at said point with the phase of a wave as it appears thereat before transmission therefrom, means to change the effective phase of one of the waves with respect to the other to roduce an instantaneous change of the indlcated comparison, thereby obtaining data from which the distance between the fixed station and the moving object may be determined, means to transmit electromagnetic waves between the moving object and a second fixed station, and means for making observations with respect to the waves so transmitted which are similar to those made with respect tothe waves transmitted between the moving object and said first station, whereby data may be obtained from which the absolute position of the moving object may be computed.

9. In a system for ascertaining the speed and direction of a moving object, means for transmitting electromagnetic waves between the moving object and a fixed station, means at one of said points for comparing the phase of a wave as it arrives at said point with the phase of a Wave as it appears thereat before transmission therefrom, means to indicate a cyclic change in the comparative phase shift of the two waves as the moving object moves through space, thereby obtaining data from which the speed of the moving object relative to the fixed station may be determined, means to transmit electromagnetic Waves between the moving object and, a second fixed station, and means for making observations with respect to the waves so transmitted which are similar to those made with respect to the waves transmitted between the moving 'obj ect and said first station, whereby the complete data obtained will enable the computation of the direction of motion and absolute speed of the moving object in such direction when its position is known. I

10. In a system for ascertaining the movement and position of a moving object, means for transmitting electromagnetic waves between a fixed station and the moving object, means associated with the moving object for observing the total phase shift undergone by a wave in its travel, means to momentarily adjust a circuit element acted upon by one of the waves until a zero indication results, so that from the observed adjustment of the circuit element the position of-the moving object may be determined within a wave length corresponding to the frequency of the observed wave, means to indicate acyclic change in the phase shift of the Wye as the moving ob ect moves through space, thereby obtaining data from which the speed of the moving object relative to the fixed station may be determined, means for transmitting electromagnetic waves between a second fixed station and the moving object, means for making observations with respect to the waves transmitted between the second fixed station and the moving object :which are similar to those made with respect to the waves transmitted between the first fixed station and the moving object, whereby the' complete data obtained will enable computation of the absolute position of the moving object, its direction of travel, and its absolute speed in such direction.

11. In a system for ascertaining the position of ,a moving object, means for transmitting electromagnetic waves between -a fixed station and a moving object, means associated with the moving object for observing the total phase shift undergone by a wave in its travel, means to momentarily adjust a circuit element acted upon by one of the waves until a zero indication results, so that from the observed adjustment the position of the moving object may be determined within a wave length corresponding to the frequency of the observed wave, means for transmitting electromagnetic waves between a second fixed station and the moving object, and means for making observations with respect to the waves transmitted between the second fixed station and the moving object which are similar to those made with respect to the waves transmitted between the first fixed station and the 100 moving object, whereby the complete data obtained will enable thecomputation of the absolute position of the moving object when the distances to the fixed stations and their direction from the moving station is known.

12. In a system for ascertaining the speed and direction of a moving object, means for transmitting electromagnetic waves between a fixed station and the moving object, means associated with the moving object for observ- 11o ing the total phase shift undergone by a wave in its travel, means to indicate a cyclic change in the phase shift of the wave as the moving object moves through space, thereby obtaining data from which the speed of the mov- I1 ing object relative to the fixed station may be determined, means to transmit electromagnetic waves between the second fixed station and the moving object, and means for making observations with respect to the waves trans- 120 mitted between the second fixed station and the moving object which are similar tot-hose made with respect to the waves transmitted between the first fixed station and the moving object, whereby the complete data obtained 125 will enable the'computation of the direction of motion and absolute speed of the moving object in such direction, when its position is known.

13. The method of ascertaining the movement and position'of a moving object, which consists 1n generating a frequency at the observing station, transmitting in both directions between the fixed and moving stations' of the moving object through space, thereby obtaining data from which the speed of the movingobjectrelativetothefixed station may be determined, and making similar observations with respect to waves transmitted between the moving object and a second fixed station, the complete data obtainedenabling the computation of the absolute position of the moving object, its direction of travel and its absolute speed in such direction.

14;. The method of ascertaining the position of a moving object, which consists in generating a frequency at the observing station, transmitting in both directions between the fixed and movingstation frequencies whose phase is definitely related to the frequency generated at the observing station, comparing the phase of the frequency generated at the observing station with the phase of a frequency which has been shifted in phase by transmission, changing the effective phase of one of the waves with respect to the other to produce a measurable instantaneous change of indication, thereby obtaining data from which the distance between the fixed station and moving object may be determined, and making similar observations with respect to waves transmitted to the moving" object and a second transmitting station whereby the absolute position of the moving obj ect may be computed.

15. The method of ascertaining the speed and direction of a moving object, which consists in generating a frequency at the observing station, transmitting in both directions between the fixed and moving station frequencies whose phase is definitely related to the frequency generated at the observing station, comparing the phase of the frequency generated at the observin station with the phase of a frequency whic has been shifted in phase by transmission, observing the cychc change in indication as relative phases of the two waves change with movement of the moving object through space, thereby obtaining data from which the speed of the moving object relative to the fixed station may be determined, and making similar observations with respect to waves transmitted between the moving object and'a second fixed station,

the complete data obtained enabling the computation of the direction of motion and absolute speed of the moving object in such direction when its position is known.

16. The method of ascertainin the movement and position of a moving 0 ject, which consists in generating a frequency at the observing station, transmitting in both directions between the fixed and moving stations frequencies whose phase is definitely related to the frequency generated at the observing station, comparing the phase'of the frequency generated at the observing station with the phase of a frequency which has been shifted in phase by transmission, shiftin the frequency of the wave generated at t e observing station through a range sufficient to change by a predetermined amount the absolute phase difierence between the compared waves, thus obtaining data from which the distance between the fixed station and moving object may be determined, observing the cyclic changes in indication as relative phases of the compared waves change with movement of the moving object through space, thereby obtainin data from which the speed of the moving 0 ject relative to the fixed station may be determined, and making similar observations with respect to waves transmitted between the moving object and a second fixed station, the complete data obtained enabling the computation of the absolute position of the moving object, its direction of travel and its absolute speed in such direction.

17. The method of ascertaining the position of a moving object, which consists in generating a' frequency at the observing station, transmitting in both directions between the fixed and moving station frequencies whose phase is definitely related'to the frequency generated at the observing station, comparing the phase of the frequency generated at the observing station with the phase of a frequency which has been shifted in phase b transmission, shifting the frequency of t e wave generated at the observing station through a range sufficient to change by a predetermined amount the observed phase difference between the compared waves, thus obtaining data from which the distance between the fixed station and moving object may be determined, and making similar observations with respect to waves transmitted between the moving object and a second fixed station whereby the absolute position of the moving object may be computed.

In testimony whereof, I have signed my name to this specification this 7th lday of December, 1927.

ESTILL I. GREEN. 

